Center for the Built Environment | October 2016

HVAC Systems

Time-Averaged Ventilation (TAV) Controls for Variable Air Volume Systems

Soazig Kaam, Paul RafteryCBEHwakong ChengTaylor EngineeringGwelen PaliagaTRC

2 Center for the Built Environment | October 2016

Zones spend majority of their time at their minimum airflow set-points

Minimum airflow set-points are typically higher than ventilation requirements

Current practice causes overcooling and wastes energy

Perceived and real problems about operating at low airflow

Background

Source: tandfonline.com

3 Center for the Built Environment | October 2016

Time-averaged ventilation principle

TAV controls the average airflow of a zone to the minimum ventilation rate required by code

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Will the occupants get enough outside air with TAV?

Total amount of outside air entering the building remains the same

TAV reduces the total amount of mixed air circulating in the building

TAV increases the proportion of outside air supplied to the zones

5 Center for the Built Environment | October 2016

Field study in Sutardja Dai Hall

Building site: All-air VAV system Single-max controls TAV implemented in 109 zones out of 138

Schedule: April 2016 Baseline period: 10 weekdays Intervention period: 10 weekdays Similar outside air temperature between

baseline and intervention periods Sutardja Dai Hall (SDH)Source: Hathaway Dinwiddie

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Field study in Sutardja Dai Hall

Cloud

TAV(python scripts)

BACnetBuilding

Management System

sMAP

Building control package

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Results: Airflow

Mean = 13%

Mean = 16%

Mean = 41%

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Results: Airflow (continued)

39% reduction

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Results: Whole building airflow

21% reduction

N = 7356Mean = 43500 cfm

N = 7542Mean = 34500 cfm

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Results: Energy savingsPower consumption during intervention period

Savings compared to baseline period

17

2120%

0

20

40

60

80

100

Supply fan power

Aver

age

elec

trica

l pow

er c

onsu

mpt

ion

[kW

]

74

96

23%

0

20

40

60

80

100

Chilled water power

Aver

age

ther

mal

pow

er c

onsu

mpt

ion

[kW

]

0.19

0.3341%

0

1

Reheat power

Aver

age

ther

mal

pow

er c

onsu

mpt

ion

[kW

]

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What about damper wear?

(a) Distance traveled by the dampers increased with TAV(b) Number of dampers direction changes reduced with TAV

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What about the sound when the damper moves?

Tests in 28 zones following ASHRAE Performance Measurement Protocol guidelines Sound levels measurements within the PMP recommended range (35-45 dB(A))

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Conclusion

TAV controls the average zone airflow to the minimum ventilation rate required by code

TAV leverages the Internet of Things platform for buildings

TAV has shown great potential for airflow and energy savings

TAV principle